Great Wall of China
Great Wall of China, world's longest wall fortification, in northern China. It extends over 1,500 mi (2,400 km), roughly following the southern border of the Mongolian plain. Construction was begun in the Ch'in dynasty (third century B.C.) to defend China against invasion from the north and mostly completed during the Ming dynasty (1368–1644). Its average height is 25 ft (7.6 m); it is wide enough (about 12 ft/3.6 m) for people on horseback to ride along it.
See also: China.